1. Field of the Invention
The present invention concerns a switch device with two operating modes, namely: a proximity sensing first operating mode and a direct mechanical action second operating mode.
It finds an advantageous, but by no means exclusive, application in the manufacture of keypads comprising a plurality of switch devices of this kind.
2. Description of the Prior Art
Many types of direct mechanical action switches have been proposed in the past, one of the simplest solutions entailing the use of an elastic capsule made from an electrically conductive material, as described in French patent application No 90 04065 (SEXTANT AVIONIQUE). The elastic capsule, in the form of a spherical dome, is usually disposed on a printed circuit board so that its perimeter is in electrical contact with one conductive area and it extends over a second conductive area electrically insulated from the first and substantially in line with the central area of the capsule.
It is clear that on applying to the capsule a pressure towards the printed circuit board the capsule is deformed until its central part touches the second area and so establishes an electrical contact between the two areas.
One particular objective of the present invention is to add to a switch of this type, which has the advantage of being extremely flat, compact and of low cost, a proximity sensing second operating mode without modifying the mechanical construction and therefore without increasing the overall dimensions and the thickness of the switch.
The simplest and most compact proximity sensing devices, namely capacitive effect proximity sensors, necessarily include an electrically conductive material sensing area mounted on a substrate and means of connecting this area an electronic circuit. Because it is necessarily disposed in line with the pushbutton of the switch, this land and its substrate are necessarily thin and flexible. Apart from the fact that it increases the thickness of the switch in any event, this solution has the drawback of being unreliable, the conductive area and/or the associated connections having a tendency to deteriorate in time. These drawbacks are considerably accentuated when it is required to construct a keypad because of the multiplicity of area, the connections between them and the large number of connecting members required.
One particular objective of the invention is to eliminate this drawback.